Measurement of $y_{CP}$ in $D^0$ meson decays to the $K_S^0{K}^{+}{K}^{-}$ final state

We present a measurement of the $D^0-{\overline{D}}^0$ mixing parameter $y_{CP}$ using a flavor-untagged sample of $D^0\to K_S^0{K}^{+}{K}^{-}$ decays. The measurement is based on a $673{\mathrm{fb}}^{-1}$ data sample recorded with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. Using a method based on measuring the mean decay time for different $K^{+}{K}^{-}$ invariant mass intervals, we find $y_{CP}=(+0.11\pm 0.61(\mathrm{stat}.)\pm 0.52(\mathrm{syst}.))\%$.

Figure 1

Projection of time-integrated Dalitz distribution to $s_0$ (solid line), and the $a_1(s_0)$ (dotted line) and $a_2(s_0)$ (dashed line) contributions for the Dalitz model given in [14].

Figure 2

(a) $(M_{{\pi }^{+}{\pi }^{-}},M_{K_S^0{K}^{+}{K}^{-}})$ distribution of selected events. (b) $M_{K^{+}{K}^{-}}$ distribution of events in the $|M_{K_S^0{K}^{+}{K}^{-}}-m_{D^0}|<10\mathrm{MeV}/c^2$ and $|M_{{\pi }^{+}{\pi }^{-}}-m_{K_S^0}|<10\mathrm{MeV}/c^2$ region (unfilled histogram), and $20<|M_{K_S^0{K}^{+}{K}^{-}}-m_{D^0}|<30\mathrm{MeV}/c^2$ and $|M_{{\pi }^{+}{\pi }^{-}}-m_{K_S^0}|<10\mathrm{MeV}/c^2$ region (filled histogram). Dashed vertical lines indicate the boundaries of ON (OFF) intervals.

Figure 3

Invariant masses $M_{K_S^0{K}^{+}{K}^{-}}$ (a) and (c), and $M_{{\pi }^{+}{\pi }^{-}}$ (b) and (d) of events passing all selection criteria for ON and OFF intervals in $M_{K^{+}{K}^{-}}$. Superimposed on the data (points with error bars) are results of the fit (solid line).

Figure 4

The $(\xi ,\zeta )$ distribution of selected events. Signal box $S$ and sideband regions $A$ and $B$ are defined in the text. Quadrants denoted by I–IV are used in the systematic uncertainty estimate, as described in Sec. 4.

Figure 5

The $s_0$ distribution of $D^0\to K_S^0{K}^{+}{K}^{-}$ decays with superimposed fit results for the eight-resonance Dalitz model given in Ref. [14]. The solid curve is the overall fitted function and the dashed curve represents the background contribution.

Figure 6

The proper decay-time distributions of all events (unfilled histogram) and background events (hatched histogram) populating the signal box $S$ for the ON and OFF intervals.